The present invention relates to a catheter for use in angioplasty procedures. Over the last two decades, the medical procedure known as angioplasty has become widely accepted as a safe and effective method for treating various types of vascular stenoses. For example, angioplasty is widely used for opening stenosis throughout the vascular system and particularly for opening stenosis in coronary artery disease. At present, the most common form of angioplasty is called percutaneous transluminal angioplasty. This procedure utilizes an elongated, more or less, flexible dilation catheter with an inflatable balloon at its distal end. Using a fluoroscope and radio opaque dye for visualization a physician may steer the distal end of the balloon catheter into position through a guide catheter and across the stenosis. Once so positioned, the dilation balloon is inflated for a brief duration to open the artery and establish adequate blood flow.
Typically, inflation of the balloon is accomplished by supplying a pressurized fluid through an inflation lumen in the catheter. The lumen is connected to an apparatus which includes a source of pressurized inflation fluid and is located outside the patient's body. Conversely, applying a negative pressure until the inflation lumen collapses the balloon to its minimal dimension allows for removal of the balloon catheter from within the target blood vessel. Such an application of negative pressure to the balloon catheter is also used to ensure that the balloon has its minimal dimension during the insertion of the balloon to the treatment site.
In the past, a number of balloon catheter designs have been developed which contribute to the safety and acceptability of the PTCA or similar medical procedures. The most common design is known as “over the wire balloon catheter”. Conventional dual lumen devices typically utilize a relatively large lumen for the passage of the guide wire and a second parallel lumen is provided for inflation and deflation of the balloon. Typically, a steerable guide wire is positioned within the larger lumen and the entire assembly is maneuvered into an initial position within the previously positioned guide catheter of large enough size to pass the balloon catheter therethrough. From here the guide wire can be rotated axially, extended or retracted into position across the lesion. The balloon dilation catheter is subsequently advanced along the guide wire in a sliding manner to position its deflated balloon across the lesion. Inflation of the balloon then effects the dilation of the stenosis. After the deflation, the deflated balloon is withdrawn in a sliding manner back in the guide catheter.
Though successful at opening stenotic lesions, this dual lumen catheter is relatively bulky and somewhat stiff as well. The technology has progressed to a point where these catheters can be used in a majority of the procedures, but the larger lumen still restricts the use of a smaller size guide catheter. These over the wire balloon catheters are difficult to use and require additional assistance or an implanting physician to control the guide wire during the positioning of the assembly because the movement of the catheter and guide wire are independent of each other. This complex coordinated activity requires both experience and skill and may result in slower insertion procedures than desired. This becomes especially important when angioplasty or stent placement are performed using distal emboli protection.
An alternative over the wire catheter assembly utilizes a non-removable guide wire that allows for longitudinal and axial movement. However, this design has a significant drawback because the entire guide wire catheter assembly must be removed to accomplish the replacement or exchange of the balloon. In some cases of PTCA, it is necessary to replace the balloon with one of a different diameter or configuration following initial dilatation. Additionally, cases of acute reclosure have been noted where the lesion re-closes following dilatation and removal of the balloon catheter. This alternative over the wire system adds to the difficulty of the subsequent procedures by requiring that the placement of the catheter renegotiate the entire vascular pathway without the advantage of the retained guide wire position. That is, when the catheter is pulled out to allow the catheter exchange, the path to the treatment site is at least partially lost because the guide wire comes out with the catheter assembly.
Another version of conventional balloon catheter is known as “monorail variance” of the standard balloon on the wire system and has been developed so that only a distal part of the balloon catheter tracks over the guide wire. These monorail catheter systems utilize a conventional balloon inflation lumen and a relatively short guiding or through-lumen for the guide wire at the distal end of the catheter. Use of this catheter involves insertion of the guide wire across the stenosis first and then advancing the monorail catheter to the stenosis site in a sliding manner. After deflation, the monorail catheter is withdrawn in the guide catheter in a sliding manner.
The principle benefits of monorail variant balloon catheters is the reduction of frictional drag over the length of the guide wire, which is external of the catheter over much of the length of the catheter, and ease of the balloon exchange. The monorail catheter provides for the ability to re-cross an acutely closed vessel or to exchange the balloon without removing or extending the guide wire. However, a disadvantage of this design is increased difficulty in steering the guide wire because the guide wire is not supported by the balloon catheter itself. Additionally, monorail catheters are at least of dual lumen configuration at the distal end. This design produces a larger profile for the catheter and a larger shaft size.
Another conventional balloon dilatation catheter design is the fixed wire or integrated “balloon on a wire dilatation catheter”. This single lumen design utilizes a guide wire having a relatively small diameter positioned within an inflation lumen and is permanently fixed to the distal end of the dilation catheter. This design produces a low profile assembly which is able to cross severely narrow lesions and to navigate tortuous vascular pathways. Additionally, the fixed guide wire is bonded to the distal end of the balloon and improves the steerability and pushability of these designs. This aspect of the fixed wire catheter also enhances their maneuverability.
The thin shaft design of the guide wire of this catheter also improves visualization and enables all but the tightest critical lesions to be crossed. However, although able to provide relatively quick and simple balloon placement as well as providing access to the lesions otherwise unsuitable for PTCA, balloon on a wire systems sacrifice both ability to maintain the guide wire position across the lesion when exchanging balloons and also the safety advantage of being able to re-cross an acutely closed vessel without repositioning the entire assembly.
In view of the deficiencies of the conventional technology, it is an object of the present invention to provide a “balloon on a wire” dilatation catheter which incorporates all the benefits of the smallest diameter “fixed wire” system and in addition, it allows for the complete removal of the balloon while maintaining the wire position. When used as a stent delivery system for primary stenting, this device will provide an extremely low profile throughout its entire length and will be extremely flexible. A distal protection device can be easily added to this system as well, which will make the entire process an easy, single step.